In vivo, three-dimensional mapping of biological tissues and vasculature is challenging because of the highly-scattering and -absorptive nature of such tissues. Optical coherence tomography (OCT) is a non-invasive imaging technology that is capable of providing high resolution, depth-resolved cross-sectional images of highly scattering samples. In addition, phase-resolved Doppler OCT (PRDOCT), a functional extension of OCT, may be used to extract velocity information about blood flow in functional vessels within the scanned tissue beds by evaluating phase differences between neighboring A-lines in an OCT B-scan frame. Recent developments in the imaging speed and sensitivity of spectral domain optical coherence tomography (SDOCT) have allowed PRDOCT to be used for in vivo imaging of blood flow, particularly in human retina. In spectral domain PRDOCT, the magnitude of Fourier transformation of the spectral interference fringes is used to reconstruct cross-sectional, structural images of the tissue sample, while the phase difference between neighboring A-scans is used to extract the velocity information of blood flow within the scanned tissue. The phase resolved method is based on the fact that the phase difference of sequential A-lines is linearly related to the flow velocity; thus, the PRDOCT method may be used to obtain quantitative information about the blood flow.
Although the PRDOCT method is of high resolution and high sensitivity to the blood flow, its imaging performance is greatly deteriorated by at least two factors: 1) the characteristic texture pattern artifact, which is caused by optical heterogeneity of the sample, and 2) the phase instability that is caused by the sample motion artifacts. The background characteristic texture pattern may be reduced in PRDOCT by using a dense-sampling approach, e.g., using more A-scans within a B-scan. This dense-sampling approach is effective in reducing the texture pattern artifacts, but it inevitably leads to a significant increase of imaging time, which is undesirable for in vivo imaging applications.
Resonant Doppler imaging may be used to minimize the influence of phase instabilities by extracting the flow information from the intensity signals without extracting the phase. Alternatively, joint spectral and time domain OCT may be used to rely on analyses of the amplitude and phase distributions of the OCT signals. However, these methods require repeated A-scans at the same lateral position, which increases the imaging time.